Enhanced Light-Harvesting and Energy Transfer in Carbon Dots Embedded Thylakoids for Photonic Hybrid Capacitor Applications.

Nanohybrid photosystems have advantages in converting solar energy into electricity, while natural photosystems based solar-powered energy-storage device is still under developed. Here, we fabricate a new kind of photo-rechargeable zinc-ion hybrid capacitor (ZHC) benefiting from light-harvesting carbon dots (CDs) and natural thylakoids for realizing solar energy harvesting and storage simultaneously. Under solar light irradiation, the embedded CDs in thylakoids (CDs/Thy) can convert the less absorbed green light into highly absorbed red light for thylakoids, besides, Förster resonance energy transfer (FRET) between CDs and Thy also occurs, which facilitates the photoelectrons generation during thylakoids photosynthesis, thereby resulting in 6-fold photocurrent output in CDs/Thy hybrid photosystem, compared to pristine thylakoids. Using CDs/Thy as the photocathode in ZHCs, the photonic hybrid capacitor shows photoelectric conversion and storage features. CDs can improve the photo-charging voltage response of ZHCs to ≈1.2 V with a remarkable capacitance enhancement of 144 % under solar light. This study provides a promising strategy for designing plant-based photonic and electric device for solar energy harvesting and storage.

Photochargeable Mn-Based Metal-Organic Framework and Decoupled Photocatalysis.

Designing multifunctional materials that mimic the light-dark decoupling of natural photosynthesis is a key challenge in the field of energy conversion. Herein, we introduce MnBr-253, a precious metal-free metal-organic framework (MOF) built on Al nodes, bipyridine linkers and MnBr(CO)3(bipyridine) complexes. Upon irradiation, MnBr-253 colloids demonstrate an electron photocharging capacity of ~42 C ⋅ g-1 MOF, with state-of-the-art photocharging rate (1.28 C ⋅ s-1 ⋅ g-1 MOF) and incident photon-to-electron conversion efficiency of ~9.4 % at 450 nm. Spectroscopic and computational studies support effective electron accumulation at the Mn complex while high porosity and Mn loading account for the notable electron storage performance. The charged MnBr-253 powders were successfully applied for hydrogen evolution under dark conditions thus emulating the light-decoupled reactivity of photosynthesis.

Carbon nitride-based light-driven microswimmers with intrinsic photocharging ability.

Controlling autonomous propulsion of microswimmers is essential for targeted drug delivery and applications of micro/nanomachines in environmental remediation and beyond. Herein, we report two-dimensional (2D) carbon nitride-based Janus particles as highly efficient, light-driven microswimmers in aqueous media. Due to the superior photocatalytic properties of poly(heptazine imide) (PHI), the microswimmers are activated by both visible and ultraviolet (UV) light in conjunction with different capping materials (Au, Pt, and SiO2) and fuels (H2O2 and alcohols). Assisted by photoelectrochemical analysis of the PHI surface photoreactions, we elucidate the dominantly diffusiophoretic propulsion mechanism and establish the oxygen reduction reaction (ORR) as the major surface reaction in ambient conditions on metal-capped PHI and even with TiO2-based systems, rather than the hydrogen evolution reaction (HER), which is generally invoked as the source of propulsion under ambient conditions with alcohols as fuels. Making use of the intrinsic solar energy storage ability of PHI, we establish the concept of photocapacitive Janus microswimmers that can be charged by solar energy, thus enabling persistent light-induced propulsion even in the absence of illumination-a process we call "solar battery swimming"-lasting half an hour and possibly beyond. We anticipate that this propulsion scheme significantly extends the capabilities in targeted cargo/drug delivery, environmental remediation, and other potential applications of micro/nanomachines, where the use of versatile earth-abundant materials is a key prerequisite.

Photorechargeable Lead-Free Perovskite Lithium-Ion Batteries Using Hexagonal Cs3Bi2I9 Nanosheets.

Materials that enable bifunctional operation in harvesting and storing energy are currently in high demand, due to their potential to efficiently use renewable solar energy. Here, we present a lead-free, all-inorganic, bismuth-based perovskite halide, which acts as a photoelectrode that can harvest energy under illumination without the assistance of an external load in a lithium-ion battery. The battery performance is shown using three different current collectors: copper, fluorine-doped tin oxide (FTO) and carbon felt (CF) to exhibit the electrode's function as a normal coin cell, as a basic photobattery with a transparent collector to elucidate its functional mechanism, and as an optimized photobattery displaying competitive metrics with other photobatteries obtaining a photo conversion efficiency of ∼0.43% for the first discharge. Upon discharging under illumination, we observed an increase in capacity from 410 to 975 mA·h·g-1. Further exploration in anode structure and design provides a path toward more efficient photobatteries.

Photo-driven Oxygen Vacancies Extends Charge Carrier Lifetime for Efficient Solar Water Splitting.

A photocharge/discharge strategy is proposed to initiate the WO3 photoelectrode and suppress the main charge recombination, which remarkably improves the photoelectrochemical (PEC) performance. The photocharged WO3 surrounded by a 8-10 nm overlayer and oxygen vacancies could be operated more than 25 cycles with 50 h durability without significant decay on PEC activity. A photocharged WO3 /CuO photoanode exhibits an outstanding photocurrent of 3.2 mA cm-2 at 1.23 VRHE with a low onset potential of 0.6 VRHE , which is one of the best performances of p-n heterojunction structure. Using nonadiabatic molecular dynamics combined with time-domain DFT, we clarify the prolonged charge carrier lifetime of photocharged WO3 , as well as how electronic systems of photocharged WO3 /CuO semiconductors enable the effective photoinduced electrons transfer from WO3 into CuO. This work provides a feasible route to address excessive defects existed in photoelectrodes without causing extra recombination.

Dynamic Evolution from Negative to Positive Photocharging in Colloidal CdS Quantum Dots.

The optical properties of colloidal semiconductor nanocrystals are largely influenced by the trapping of charge carriers on the nanocrystal surface. Different concentrations of electron and hole traps and different rates of their capture to the traps provide dynamical charging of otherwise neutral nanocrystals. We study the photocharging formation and evolution dynamics in CdS colloidal quantum dots with native oleic acid surface ligands. A time-resolved technique with three laser pulses (pump, orientation, and probe) is developed to monitor the photocharging dynamics with picosecond resolution on wide time scales ranging from picoseconds to milliseconds. The detection is based on measuring the coherent spin dynamics of electrons, allowing us to distinguish the type of carrier in the QD core (electron or hole). We find that although initially negative photocharging happens because of fast hole trapping, it eventually evolves to positive photocharging due to electron trapping and hole detrapping. The positive photocharging lasts up to hundreds of microseconds at room temperature. These findings give insight into the photocharging process and provide valuable information for understanding the mechanisms responsible for the emission blinking in colloidal nanostructures.

Single-Particle Ratiometric Pressure Sensing Based on "Double-Sensor" Colloidal Nanocrystals.

Ratiometric pressure sensitive paints (r-PSPs) are all-optical probes for monitoring oxygen flows in the vicinity of complex or miniaturized surfaces. They typically consist of a porous binder embedding mixtures of a reference and a sensor chromophore exhibiting oxygen-insensitive and oxygen-responsive luminescence, respectively. Here, we demonstrate the first example of an r-PSP based on a single two-color emitter that removes limitations of r-PSPs based on chromophore mixtures such as different temperature dependencies of the two chromophores, cross-readout between the reference and sensor signals and phase segregation. In our approach, we utilize a novel "double-sensor" r-PSP that features two spectrally separated emission bands with opposite responses to the O2 pressure, which boosts the sensitivity with respect to traditional reference-sensor pairs. Specifically, we use two-color-emitting dot-in-bulk CdSe/CdS core/shell nanocrystals, exhibiting red and green emission bands from their core and shell states, whose intensities are respectively enhanced and quenched in response to the increased oxygen partial pressure that effectively tunes the position of the nanocrystal's Fermi energy. This leads to a strong and reversible ratiometric response at the single particle level and an over 100% enhancement in the pressure sensitivity. Our proof-of-concept r-PSPs further exhibit suppressed cross-readout thanks to zero spectral overlap between the core and shell luminescence bands and a temperature-independent ratiometric response between 0 and 70 °C.

Near-infrared-II photocharging nanozyme for enhanced tumor immunotherapy.

In tumor therapy, copper (Cu)-based nanozymes with peroxidase-like activity play a crucial role in converting hydrogen peroxide into hydroxyl radicals (OH). This process induces immunogenic cell death, which in turn activates the body's immune response, enhancing the efficacy of tumor immunotherapy. Nonetheless, the efficiency of this reaction is curtailed due to the oxidation of Cu(I) to Cu(II), leading to the self-depletion of the nanozyme's activity and an insufficient yield of OH for effective immunotherapeutic activation. To surmount this challenge, our research introduces a photocharging self-doped semiconductor nanozyme, copper sulfide (Cu9S8). The photocharging effect enables the nanozyme to convert internal Cu(II) back to Cu(I) through charge transfer induced by near-infrared (NIR)-II photothermal energy, thereby effectively maintaining the enzyme-like activity of the nanozyme. Additionally, Cu9S8 is enhanced with a calcium sulfide (CaS) coating. This coating reacts in the acidic microenvironment of tumors to generate hydrogen sulfide (H2S) gas, which in turn suppresses the catalase activity inherent in tumor cells, ensuring a plentiful supply of H2O2 for the nanozyme's operation. This dual strategy of amplifying enzyme-like activity and substrate availability culminates in the generation of ample OH within tumor cells, leading to significant immunogenic cell death and thereby realizing potent immunotherapy.

Synthesis of N-Doped Graphene Photo-Catalyst for Photo-Assisted Charging of Li-Ion Oxygen Battery.

In this work, nitrogen (N)-doped graphene film is synthesized, as a photo-catalyst, on one side of the copper foam by chemical vapor deposition and the copper foam is directly used as an electrode after porous Pd@rGO cathode loading to the other side of the foam for the photo-assisted charging of the Li-ion oxygen battery. The amount of urea (CO(NH2)2), which is used as N atom source, is optimized to get maximum photo-anodic currents from the n-type graphene films. The optical band gap and the valance band edge potential of the optimized N-doped graphene film are determined as 2.00 eV and 3.71 VLi+/Li, respectively. X-ray photoelectron spectra provided that the atomic percent of N atoms in the graphene film is 1.34% and the graphitic, pyrrolic and pyridinic N atom percentages are 54.01%, 42.20% and 3.79%, respectively. The photo-assisted charging tests indicated that the N-doped graphene film photo-catalyst reduced the charging potential significantly even at 1000 mA g-1 (0.1 mA cm-2) current density and improved the cyclic discharge-charge performance of the Li-ion oxygen battery considerably.

Realizing Unassisted Photo-Charging of Zinc-Air Batteries by Anisotropic Charge Separation in Photoelectrodes.

Solar rechargeable zinc-air battery is a promising approach for capturing and storing intermittent solar energy through photoelectrochemical reactions. However, unassisted photo-charging of zinc-air batteries is challenging due to suboptimal carrier accumulation on photoelectrodes, resulting in sluggish reaction kinetics. Here, unassisted photo-charging of zinc-air battery is achieved by investigating anisotropic photogenerated charge separation on a series of representative semiconductors (ZnIn2 S4 , TiO2 , and In2 O3 ), among which the exceptional anisotropic charge separation on a ZnIn2 S4 photoelectrode is revealed based on anisotropic charge diffusion capabilities. The charge separation is facet-dependent, which is observed using Kelvin probe force microscopy, verifying a cause-and-effect relationship between the photo-charge accumulation on photoelectrodes and their photo-charging performance in zinc-air batteries. This work achieves an unassisted photo-charging current density of 1.9 mA cm-2 with a light-to-chemical energy conversion efficiency of 1.45%, highlighting the importance of anisotropic semiconductors for unassisted photo-charging of zinc-air batteries via efficient photogenerated charge separation.

Photoassisted Charging of Li-Ion Oxygen Batteries Using g-C3N4/rGO Nanocomposite Photocatalysts.

In this work, g-C3N4/rGO nanocomposites were synthesized to use them as photocatalysts in Li-ion oxygen batteries by aiming at the reduction of the charging potential efficiently under photoassisted conditions. Fourier transform infrared (FTIR) spectra showed that novel C═C bonds formed between g-C3N4 and rGO during the decomposition of melamine and that the formation of these bonds was assumed to cause a red shift in the optical absorption band edge. The competition between the narrowing in the optical band gaps of the nanocomposites as a result of the red shift due to the presence of rGO and the degradation in the visible light utilization as a result of favorably absorbed incident light by rGO instead of g-C3N4 pointed out that the g-C3N4/3% rGO nanocomposite has the optimum light absorbance efficiency. The photoassisted charging tests indicated that the g-C3N4/3% rGO nanocomposite reduced the charging potential effectively, especially at higher current densities, and improved the cyclic discharge-charge performance of the Li-ion oxygen batteries considerably.

Continuous photocatalysis via photo-charging and dark-discharging for sustainable environmental remediation: Performance, mechanism, and influencing factors.

Continuous photocatalysis via photo-charging and dark-discharging presents a paradigm shift in conventional photocatalysis with the requirement of continuous illumination to maintain the catalytic activity. This is expected to meet the ever-increasing demand for sustainable development of energy and environment driven by natural day-night cycles. Substantial advances in continuous photocatalysis for various environmental applications under light-dark cycles have been witnessed during the last decade. However, there lacks a systematic and critical review on basic but important information of continuous photocatalysis for environmental remediation, challenging robust scientific progress of this technology towards potential practical use. Here, the general description of continuous photocatalysis involving energy storage mechanisms (hole and electron storage) and characterizations (electron storage behaviors, release behaviors and storage capacity) has been first introduced. Importantly, the remediation performance and mechanism of continuous photocatalysis for environmental applications are qualitatively and quantitatively demonstrated, including chemical pollutant oxidation and reduction, microbial pathogen inactivation, and multifunctional treatment. In addition, key factors influencing its remediation performance are analyzed, for the first time, from both operational and environmental views. The ample opportunities in the field of continuous photocatalysis for sustainable environmental remediation are also pointed out, calling for more efforts to fill current knowledge gaps in the future.

Multisite PCET with photocharged carbon nitride in dark.

A combination of photochemistry and proton coupled electron transfer (PCET) is a primary strategy employed by biochemical systems and synthetic chemistry to enable uphill reactions under mild conditions. Degenerate nanometer-sized n-type semiconductor nanoparticles (SCNPs) with the Fermi level above the bottom of the conduction band are strongly reducing and act more like metals than semiconductors. Application of the degenerate SCNPs is limited to few examples. Herein, we load microporous potassium poly(heptazine imide) (K-PHI) nanoparticles with electrons (e‒) and charge balancing protons (H+) in an illumination phase using sacrificial agents. e‒/H+ in the K-PHI nanoparticles are weakly bound and therefore could be used in a range of PCET reactions in dark, such as generation of aryl radicals from aryl halides, ketyl radicals from ketones, and 6e‒/6H+ reduction of nitrobenzene to aniline. The integration of several features that until now were intrinsic for plants and natural photosynthesis into a transition metal free nanomaterial composed of abundant elements (C, N, and K) offers a powerful tool for synthetic organic chemistry.

Environmentally Compatible Lead-Free Perovskite Solar Cells and Their Potential as Light Harvesters in Energy Storage Systems.

Next-generation renewable energy sources and perovskite solar cells have revolutionised photovoltaics research and the photovoltaic industry. However, the presence of toxic lead in perovskite solar cells hampers their commercialisation. Lead-free tin-based perovskite solar cells are a potential alternative solution to this problem; however, numerous technological issues must be addressed before the efficiency and stability of tin-based perovskite solar cells can match those of lead-based perovskite solar cells. This report summarizes the development of lead-free tin-based perovskite solar cells from their conception to the most recent improvements. Further, the methods by which the issue of the oxidation of tin perovskites has been resolved, thereby enhancing the device performance and stability, are discussed in chronological order. In addition, the potential of lead-free tin-based perovskite solar cells in energy storage systems, that is, when they are integrated with batteries, is examined. Finally, we propose a research direction for tin-based perovskite solar cells in the context of battery applications.

Photocharging and Band Gap Narrowing Effects on the Performance of Plasmonic Photoelectrodes in Dye-Sensitized Solar Cells.

The incorporation of plasmonic nanostructures in active electrodes has become one of the most attractive ways to enhance the photoconversion efficiency (PCE) of dye-sensitized solar cells (DSSCs). Although an enhancement of PCE because of the incorporation of plasmonic nanostructures of different sizes, either bare or coated, has been demonstrated, the fundamental mechanisms associated to such enhancement are still unclear. Besides, the photocurrent enhancement of plasmonic DSSCs is frequently associated to the strong surface plasmon resonance (SPR) absorption of metal nanoparticles. In this work, through oxygen K-edge soft X-ray absorption and emission spectroscopies of plasmonic electrodes and electrodynamical characterization of the fabricated cells, we demonstrate a band gap narrowing and photocharging effect on the plasmonic electrodes that definitely contribute to the PCE enhancement in plasmonic DSSCs. The incorporation of bare metal nanoparticles in active metal-oxide semiconductor electrodes such as TiO2 in optimum concentration causes an upward shift of its valence band edge, reducing its effective band gap energy and enhancing the short-circuit current of DSSCs. On the other hand, small perturbation-based stepped light-induced transient measurements of photovoltage and photocurrent of the operating DSSCs revealed an upward shift of quasi-Fermi level of photoelectrodes because of the photocharging effect induced by the incorporated metal nanoparticles. The upward shift of the quasi-Fermi level causes an increase in open-circuit voltage ( VOC), nullifying the effect of band gap reduction. The short-circuit photocurrent enhancement was controlled by the band gap narrowing, screening the SPR contribution. The results presented in this work not only clarify the contribution of SPR absorption in plasmonic DSSCs, but also highlight the importance of considering the corrections in the effective base voltage because of the quasi-Fermi level band shift during the estimation of the transport and recombination parameters of an assembled DSSC.

Understanding Photocharging Effects on Bismuth Vanadate.

Bismuth vanadate (BiVO4) is a promising material for photoelectrochemical water oxidation. Recently, it has been shown that "photocharging" BiVO4 results in an improved water oxidation performance. However, the understanding of how BiVO4 is being improved has been lacking. Here we study the surface kinetics of BiVO4 using intensity-modulated photocurrent spectroscopy and show that photocharging BiVO4 results in both surface and bulk improvements. This result sheds light on how the surface charge transfer and bulk charge transport of BiVO4 respond to illumination.